With the advent of electronic equipment, radio frequency (“RF”), microwave, and millimeter wave circuits are common. As telecommunication systems continue to advance, there is a constant need to increase the bandwidth, speed, efficiency, and miniaturization of new telecommunication devices while constantly increasing the quality of the telecommunication devices and reducing the manufacturing costs.
Typically, telecommunication devices, and electronic equipment in general, include numerous types of electronic components and circuits including directional couplers and directional bridges. Generally, directional couplers and directional bridges are electronic devices utilized in RF, microwave, and millimeter wave signal routing for isolating, separating or combining signals. Typically, directional couplers are utilized as impedance bridges for microwave and millimeter wave measurements and for power monitoring.
Directional couplers and directional bridges (generally known as “directional circuits”) are usually three-port or four-port devices/circuits that have a signal input port (from a source) and a signal output port (to a load) and at least one coupled port whose output is proportional to either the incident wave (from the source) or the reflected wave (from the load). It is appreciated by those skilled in the art that it is common practice in RF, microwave, and millimeter wave engineering to consider an electrical signal in an electronic circuit/device as the sum of an incident and a reflected traveling wave to and from a source and load, respectively, relative to a characteristic impedance Z0 of the electronic circuit/device (typically about 50 ohms). A directional circuit generally separates a transmitted signal into the detection circuit or coupled port based on the direction of the signal propagation. There are many uses for these directional circuits including network analysis and monitoring the output signal levels of a traveling wave incident on a load.
At present, there are numerous approaches to implementing a directional circuit. One example is to implement a directional coupler as a device that has a physical length over which two transmission lines couple together electromagnetically or that utilizes the phase shift along a length of transmission line. Another example approach (known as a directional bridge) may utilize lumped elements that may include transformers and resistors.
In FIGS. 1 and 2, an example of an implementation of known directional couplers 100 is shown. The directional coupler 100 may include three ports such as a signal input port (“port A 102”), a signal output port (“port B 104”), and at least one coupled port (“port C 106”). The directional coupler 100 may be in signal communication with a signal source 108 via signal source impedance (“Zsource”) 110, and a load having a load impedance (“Zload”) 112. As an example of operation, the directional coupler 100 may be utilized to unequally split the signal 114 flowing in from the load at port B 104 while simultaneously fully passing the signal 116 flowing in from the opposite direction from the source 108 into port A 102. Ideally the signal 114 flowing in from the load at port B 104 will pass to the coupled port C 106 and appear as coupled signal 118. Similarly, an input signal 120 at port C 106 would pass to port B 104. However, port A 102 and port C 106 are isolated in that any signal 116 flowing into port A 102 will not appear at port C 106 but will propagate through to port B 104. Additionally, port B 104 is isolated from port A 102 because any signal 114 from port B 104 will flow to port C 106 not port A 102. In FIG. 2, an example of an implementation of the known directional coupler 100 is shown utilizing two transformers T1 and T2 and a resistor R.
Unfortunately, directional couplers have the disadvantage that they are typically too large to be practical for an integrated circuit (“IC”) except at very high frequencies because at low frequencies approaching direct current (“DC”) they are typically too large to be practical for many electronic instruments. As an example, directional couplers are usually limited by size limitations to low frequency operation of about 10 megahertz (“MHz”) in most electronic devices.
Attempts to solve this problem include utilizing directional bridges because directional bridges typically operate at lower frequencies than directional couplers. However, while directional bridge may typically operate in the kilohertz (“KHz”) frequency range, they still unfortunately do not operate at low frequencies approaching DC. Additionally, similar to known directional couplers, known directional bridges are not suitable for integration on ICs because directional bridges generally utilize transformers which are difficult to implement with known IC technologies particularly at low frequencies. Moreover, typically broadband instrument grade directional couplers and conventional directional bridges are implemented with expensive precision mechanical parts and assemblies and typically require hand assembly and adjustment.
Therefore, there is a need for a new direction circuit/device capable of operating continuously from DC up to high frequencies in the millimeter wave range while being simple to integrate with known IC technologies.